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December 13, 2022

USGS scientists of the Eastern Ecological Science Center and the Forest and Rangeland Ecosystem Science Center published new findings on environmental contaminants to assist the National Park Service and Yurok Tribe in management of the California condor (Gymnogyps californianus), one of the rarest avian scavengers in the world.

Image: Endangered California Condor
An endangered California condor flies over the Bitter Creek National Wildlife Refuge, California. USGS scientists are helping managers understand how California condors use their habitat, gaining valuable information that will help inform not only which potential energy development sites are likely to have the least impact on condors but also which areas of Oregon might be most suitable for future reintroductions of this large, endangered bird. 

Did you know? Some USGS scientists study how chemicals used to control pest species like rats and mice may have unintended consequences for other animals, including birds.

Anticoagulant rodenticides are widespread environmental contaminants that pose risks to predatory and scavenging birds because they routinely occur within their prey, causing secondary poisoning. The occurrence of anticoagulant rodenticides within food webs can increase the likelihood of non-target exposure and potential adverse effects in predatory and scavenging birds. However, little is known about anticoagulant rodenticide exposure in one of the rarest avian scavengers in the world, the California condor (Gymnogyps californianus).

USGS researchers of the Eastern Ecological Science Center and the Forest and Rangeland Ecosystem Science Center recently collaborated with the National Park Service and Yurok Tribe to assess contaminant exposure in California condors and surrogate turkey vultures (Cathartes aura) in California, Arizona and Oregon. This study aimed to gauge current exposure to anticoagulant rodenticides throughout the central/southern California and Arizona flocks, and potential hazards of these rodenticides to a proposed future condor flock at a newly established release site in northern California by determining how application rate and environmental factors influence exposure. Additionally, researchers examined whether anticoagulant rodenticide exposure might be associated with prolonged blood clotting time and potential mortality in condors.

This study was among the first and most widespread assessments of anticoagulant rodenticide exposure in California condors, detailing the incidence rate of exposure as well as some potential factors that influence the probability of exposure and liver residue concentrations. Only the more persistent and more toxic “second-generation” rodenticides were detected in livers, but exposure was detected in all condor flocks and 42% of the condors. There was evidence of prolonged blood clotting time in 16% of the free-flying condors, potentially indicative of recent exposure to short-lived “first-generation” anticoagulant rodenticides.

The ongoing recovery to the California condor is an example of how various wildlife management activities including captive propagation and mitigation of environmental hazards can save a species on the brink of extinction. Management and recovery of California condors is dependent on understanding risks to individuals, flocks, and the overall population. Anticoagulant rodenticide exposure appears to be common in all current condor flocks within the United States and there is potential for exposure in the newly established free-flying flock in northern California. In addition, the combined effects of long-term exposure to anticoagulant rodenticides and multiple other contaminants such as lead remain poorly understood in condors. Further elucidating where on the landscape condors are being exposed to anticoagulant rodenticides would also help in developing plans for mitigating exposure, helping to ensure we have healthy populations of condors for generations to come.

Two graphs overlaid on a photo of a California condor feeding on a wild pig carcass
A California condor feeds on a wild pig carcass near Pinnacles, National Park, CA. The graphs overlayed with the image show exposure of condors to second generation anti-coagulant rodenticides during 2009-2017 (left) and the response of rodenticide exposure to local precipitation (right).

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